By Ewan Murray When the debate arises over the greatest of all time, only two names normally crop up: Lionel Messi and Cristiano Ronaldo. The two superstars are undoubtedly the best players the 21st century has seen and have often had to share the limelight as they attempted to one-up each other on the field with their genius. While their powers have waned in recent years, they still steal attention wherever they go. Few arguments are fought as fiercely when it comes to crowning one of these heavyweights as the greatest fans have ever seen, with their brilliance often splitting opinion. So, wi…